1. Field of the Invention
The present invention relates to methods and apparatuses for recycling ultraviolet curing resins that are in a colored, uncured state, and to methods for manufacturing optical recording media using those recycling methods.
2. Background Information
After light curing, ultraviolet curing resins are capable of expressing multiple functionality through the action of photopolymerizable monomers, photopolymerizable oligomers and various additives contained in the resins. Moreover, they are widely used in a variety of applications because of advantages such as low temperature curability and mass producibility.
If the uncured state of an ultraviolet curing resin is a liquid, then as the conventional method for recycling ultraviolet curing resins, it has been standard practice to recover the residual resin from the manufacturing process while it is still in the liquid state, and use it after removing foreign matter by filtering through a filter, for example.
Ultraviolet curing resins are used in optical recording media for substrate adhesion and for protecting the constituent layers and the like. As a method for re-using ultraviolet curing resins in the manufacture of optical recording media, it has been standard practice to remove foreign matter by filtering. (See Japanese Unexamined Patent Publication No. H08-7347A).
Furthermore, write-once optical recording media that use dye components in the recording layer have a structure in which the recording layer is formed on the substrate, and information is recorded by irradiating laser light from the substrate side. The dye component that forms the recording layer absorbs the irradiated laser light and causes a thermal change such as heating, melting, decomposition or vaporization, and as a result, the recording occurs by physical changes such as deformation of the substrate or changes to the dye. Furthermore, the recorded information is reproduced by reading changes in the reflectivity of the parts in which physical changes have occurred and the parts where they have not occurred, due to the laser light.
Dyes such as metal containing azo-based dyes, which are chelated compounds of azo compounds and metals, cyanin-based dyes and phthalocyanin-based dyes are readily available as the dye material used here. Of these, optical recording media that are recorded by absorbing laser light having a wavelength of 630 to 660 nm have undergone particular development and investigation, and are the standard for 1 to 8 speed recording DVD-R media. It is anticipated that DVD-R media will be developed to handle high speed recording in the future, and will undergo rapid commercial expansion in conjunction with recording drives in a similar manner to the development of CD-Rs.
In the manufacture of write-once optical recording medium in which dye components are used, a recording layer made of the dye component is formed on the substrate after which the excess portion of the dye component is removed by a process such as washing. The medium then passes through a process of film formation of a reflective layer, and then an adhesive layer or protective layer is formed using an ultraviolet curing resin. The photopolymerizing monomer or the photopolymerizing oligomer, which is the principal component of the ultraviolet curing resin, contains multiple varieties of functional groups in its molecular structure, and thus it is immediately colored when the ultraviolet curing resin contacts the small amount of dye component residual on the optical recording medium.
In the process of film forming the ultraviolet curing resin, it is necessary to reject excess resin caused by overrun in order to prevent visual flaws such as air bubbles, and to ensure mechanical properties.
As a method for recycling the ultraviolet curing resin, an example is known in which the rejected resin is collected, added to the unused mother liquor, diluted to a level that maintains the characteristics, and then used (see Japanese Unexamined Patent Publication No. 2001-184732A).
However, in JP H08-7347A, with these methods there is no improvement to the color, even if foreign matter such as grit are removed. Furthermore, in No. 2001-184732A, it is necessary to confirm the concentration of the contaminating dye, and thus there is a risk that the process will become too complex and cause a drop in productivity. Furthermore, conventional methods have been insufficient if the colorability of the contaminating dye is high, or due to the solution's shade, the waste solution must be disposed, because the method disclosed in No. 2001-184732A cannot be used because there is a risk of compromising the product quality even due to a minute quantity of dye, thus making the solution unusable.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need to simplify the recycling of an ultraviolet curing resin that is in an uncured state, and that has been colored by mixing with another substance, particularly an organic compound, so as to reduce costs and to contribute to reducing the burden of waste solution treatment on the environment.